For years, oil and gas drillers have insisted that it would be physically impossible for fracking chemicals to travel upwards from deep shale layers to shallow aquifers because of the thick layers of solid rock that separate the two. A new peer-reviewed study offers contradictory evidence. The study, sponsored by environmental advocates and published in the journal Ground Water, found that fracking can indeed cause chemicals to migrate upwards through cracks and fissures and contaminate groundwater in the Marcellus shale.

Using computer modeling, Tom Myers, the author of the study, used data from the Marcellus shale and concluded that the pressures created by fracking can persist for up to six years and can speed up natural processes that slowly drive fluids towards the surface. “If contaminants reach natural fractures under pressure, the upward flow has the potential to be enhanced greatly,” Myers, the study’s author, told Bloomberg. “It can flow upward if there’s a pathway and unless it’s completely impermeable, there’s always a pathway. It’s just a question of how long it takes.”

Natural gas industry advocates say that the thousands of vertical feet of rock between shale formations and aquifers create a barrier that makes it impossible for toxic chemicals to migrate into groundwater supplies. But the evidence that fracking can contaminate groundwater supplies has been rising. The U.S. Environmental Protection Agency (EPA) concluded as early as 1987 that fracking fluids have indeed migrated from drilled wells into aquifers, The New York Timesreported last August. State and federal regulators concluded that this was how one family’s drinking water was contaminated in West Virginia in 1984.

One of the biggest problems for researchers has been that the oil and gas industry often reaches sealed settlements with people whose drinking water was rendered undrinkable, so documentation is under wraps, the EPA pointed out at the time. The result is that the public, including scientists and regulators, are prevented from knowing about cases where groundwater has been contaminated.

During fracking, drillers inject millions of gallons of sand, water and chemicals under high pressures to shatter the shale rock layer and free trapped natural gas. The fractures created during this process can extend long distances, sometimes nearly half a mile, in ways that engineers say can be complex and difficult to predict.

Not only are there natural fractures and those created during fracking, but drilling is often done near abandoned natural gas wells, which The Times found are poorly monitored in many states. Improperly capped abandoned wells may serve as paths for fracking fluids to move upwards towards aquifers.

Much of the political debate about fracking has centered on the ability of fluids to migrate below ground, in part because industry advocates have repeatedly claimed that there has not been a single case of groundwater contamination resulting directly from fracking, as opposed to other parts of the extraction process like drilling or disposing of wastewater, and therefore fracking should be left unregulated by the federal government. But there are countless documented cases of water pollution from the overall oil and gas drilling process. This contamination more often than not is from above-ground spills. Natural gas can also leak from poorly cased gas wells and ending up in peoples’ water supplies. The disposal of billions of gallons of drilling waste is a huge and growing threat to drinking water as well.

And increasingly, the industry’s claim that fracking is not responsible has been called into question by scientific evidence. The new study, which was paid for by Catskill Mountainkeeper and the Park Foundation, two upstate New York organizations that have opposed gas drilling and fracking in the Marcellus, is important because it adds research to an area that has been woefully lacking in scientific study. Some regulators predict that in the next decade or so there will be more than 100,000 new oil or gas wells fracked. But there has been a relative dearth of rigorous research on what actually happens underground when thousands of pounds of pressure are applied to millions of gallons of chemicals and water to release the fossil fuels trapped in shale formations.

The study in Ground Water does not describe instances where pollution from fracking has occurred in the real world, but instead uses modeling to show that it is theoretically possible—and that it can happen relatively soon after a well is fracked. Natural gas is not the only substance trapped within the shale layer and freed up by fracking. There is also briny water, laced with corrosive salts and carrying naturally occurring radioactive materials.

The researchers concluded that fracking will dramatically speed up the movement of this material, combined with the chemicals that drillers inject into the ground. Their models indicated that fluids could travel distances would take tens of thousands of years under natural conditions within a single century. The researchers added that when they factored in the Marcellus’ many natural faults and fractures, fluids could move 10 times as fast.

The researchers added that the pressure from drilling—one of the main drivers that moves the chemicals from down deep up toward the aquifers—continues even after drilling and fracking have stopped. It can take three to six years before the artificial pressure from the drilling process wears away and the natural balance of pressure is restored, the study found.

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